1. Field of the Invention
The present invention relates to a lens barrel, and more particularly, to a lens barrel used in a camera and an optical apparatus that enables a lens to move in an optical axis direction.
2. Description of the Related Art
In a conventional lens barrel used in a digital camera and the like, a mechanism of moving a lens in an optical axis direction includes a cam barrel that is provided with a cam groove and a lens holder having a lens and a cam pin, as illustrated in FIG. 14 of Japanese Patent Application Laid-Open No. 2008-58581.
In the conventional lens barrel, if the cam barrel rotates, the cam pin engaged with the cam groove at an inner circumference of the cam barrel is guided by an advance key along a lift of the cam groove and moved in the optical axis direction. As a result, the lens holder moves in the optical axis direction.
Further, in the mechanism that moves the lens in the optical axis direction, instead of the cam pin, a ball may be engaged with the cam groove, as discussed in Japanese Patent Application Laid-Open No. 05-333255.
However, in the lens barrel using the cam pin described in Japanese Patent Application Laid-Open No. 2008-58581, a driving load of the lens barrel may easily increase due to friction caused by line contact of the cam pin and the cam groove, when the lens is driven.
When the driving load of the lens barrel is large, a speed reduction ratio of a speed reduction gear train that connects a motor for driving the lens barrel and the lens barrel needs to be increased to increase driving torque. For this reason, if the lens barrel is driven at the same number of motor rotations as that of the lens barrel which shows a small driving load, a driving time of the lens barrel needs to be increased.
Further, if the lens barrel is driven at the number of motor rotations higher than that of the lens barrel which shows the small driving load to avoid an increase in the driving time of the lens barrel and equalize the driving time, driving noise of the lens barrel is increased.
Further, a backlash dealing with a component error may be set in advance to an engaging portion of the cam pin and the cam groove to reduce the driving load of the lens barrel caused by the component error. In this configuration, however, a problem occurs in keeping satisfactory precision of the lens.
Further, in the lens barrel using the ball instead of the cam pin as a follower, a ball follower may be dislocated from the cam groove due to an external force.
Accordingly, the lens barrel having the above configuration may be used only in a portion where the external force is not applied to, as described in Japanese Patent Application Laid-Open No. 05-333255.